utils/cpp: add IsAHash function

This function is mainly used to check that the hash of a Digest
received over the wire is a real hash, to prevent a malicious attack.

2 files changed, 42 insertions, 0 deletions

diff --git a/src/utils/cpp/TARGETS b/src/utils/cpp/TARGETS
index 7c05472f..578996b2 100644
--- a/src/utils/cpp/TARGETS
+++ b/src/utils/cpp/TARGETS
@@ -88,4 +88,11 @@
   , "hdrs": ["path_hash.hpp"]
   , "stage": ["src", "utils", "cpp"]
   }
+, "verify_hash":
+  { "type": ["@", "rules", "CC", "library"]
+  , "name": ["verify_hash"]
+  , "hdrs": ["verify_hash.hpp"]
+  , "deps": [["@", "fmt", "", "fmt"]]
+  , "stage": ["src", "utils", "cpp"]
+  }
 }
diff --git a/src/utils/cpp/verify_hash.hpp b/src/utils/cpp/verify_hash.hpp
new file mode 100644
index 00000000..ab2a4b45
--- /dev/null
+++ b/src/utils/cpp/verify_hash.hpp
@@ -0,0 +1,35 @@
+// Copyright 2023 Huawei Cloud Computing Technology Co., Ltd.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef INCLUDED_SRC_UTILS_CPP_VERIFY_HASH_HPP
+#define INCLUDED_SRC_UTILS_CPP_VERIFY_HASH_HPP
+#include <algorithm>
+#include <cctype>
+#include <optional>
+#include <string>
+
+#include <fmt/core.h>
+/// \brief Check if the passed string \p s is a hash.
+/// This function is mainly used to check that the hash of a Digest received
+/// over the wire is a real hash, to prevent a malicious attack.
+[[nodiscard]] static inline auto IsAHash(std::string const& s) noexcept
+    -> std::optional<std::string> {
+    if (!std::all_of(s.begin(), s.end(), [](unsigned char c) {
+            return std::isxdigit(c);
+        })) {
+        return fmt::format("Invalid hash {}", s);
+    }
+    return std::nullopt;
+}
+#endif